1. Field of The Invention
The present invention relates to a filter element, and more particularly, to a filter element mounted to an air cleaner, an oil strainer or like applicable to an internal combustion engine.
2. Related Art
There is known, in a conventional technology, a filter element provided with a filter member that is formed by folding a non-woven fabric (unwoven cloth) or filter paper along a width direction thereof to provide pleated-shape (which may be called hereinafter pleated filter member or merely filter member) and a holder frame that holds or supports an outer edge portion of the pleated filter member.
As a prior art patent document, there is provided, for example, Japanese Patent Laid-open Publication No. 2002-273116 (Patent Document 1). A filter element disclosed in this Patent Document 1 is a filter element that is provided with a pleated filter member and a reinforcing rib made of synthetic resin formed integrally with the filter member. The reinforcing rib is provided so as to extend from one end to the other end of the filter element in a direction perpendicularly intersecting a pleated direction on the center line of the pleated side line of the filter member except a peripheral edge portion of the filter member.
As described above, the filter element disclosed in the Patent Document 1 is formed from a frame body or frame member integrally formed with the peripheral edge portion of the filter member and a reinforcing rib extending from one end to the other end of the filter member in the pleated direction except the peripheral edge portion thereof with the synthetic resin integrally with each other. According to this structure, it becomes possible to prevent close-contact or direct-contact of adjacent gathers of the pleated lines at a fluid-flow time, thereby keeping large effective filtrating area and maintaining the pleated shape and rigidity of the frame body.
The filter element described above is formed from the frame body and the reinforcing rib which are formed integrally with the same synthetic resin, and when the frame body and the reinforcing rib are formed by injection molding process, the filter member is manufactured by insert-molding process.
According to the insert-molding process, since the filter member is disposed in a mold, the mold is clamped, and then, synthetic resin fused in the mold is injected, the filter member and the reinforcing rib can thus be integrally formed. In this method, since the filter member and the reinforcing rib can be simultaneously formed, the number of parts or steps of manufacturing working can be eliminated or decreased, contributing to cost saving.
However, in the case of insert-molding the filter member formed of a filter paper or non-woven fabric, there cases a case such that a synthetic resin fused in the injection-molding process seeps into the filter member through boundary of the frame body or the reinforcing rib by injection pressure, and thereby, the seeped fused synthetic resin protrude as burrs on the surface of the filter member, which constitutes an obstacle for ensuring an effective filtrating area. In order to obviate such defect, there is proposed a countermeasure such that the boundary of the frame body or the reinforcing rib is compressed by using a mold to prevent the fused synthetic resin from seeping from the boundary of the frame body or the reinforcing rib or from protruding on the surface of the filter member.
In the thus formed filter element, a portion of the filter member compressed by the mold is clogged, which results in increasing in resistance against filtration, and hence, reducing the effective filtrating area, thus providing a problem. More particularly, in the filter element in which the reinforcing rib is formed integrally with the filter member, it is necessary to compress both the sides of the reinforcing rib, and accordingly, an area to be compressed increases, which leads enlargement of the filter element in size and results in difficulty for ensuring an effective filtrating area without enlarging the filter element.